Cisco IOS XR Software Releases 3.3.0 to 4.2.0 contain a vulnerability when handling fragmented packets that could result in a denial of service (DoS) condition of the Cisco CRS Route Processor cards listed in the "Affected Products" section of this advisory.

The vulnerability is due to improper handling of fragmented packets. The vulnerability could cause the route processor, which processes the packets, to be unable to transmit packets to the fabric.

Customers that are running version 4.2.1 or later of Cisco IOS XR Software, or that have previously installed the Software Maintenance Upgrades (SMU) for Cisco bug ID CSCtz62593 are not affected by this vulnerability.

Cisco has released free software updates that address this vulnerability.

To determine the Cisco IOS XR Software release that is running on a Cisco product, administrators can log in to the device and issue the show version command to display the system banner. The system banner confirms that the device is running Cisco IOS XR Software by displaying text similar to Cisco IOS XR Software. The software version is displayed after the text "Cisco IOS XR Software".

The following example identifies a Cisco CRS series device that is running Cisco IOS XR Software Release 4.0.4:

To determine whether a Cisco CRS series device with affected software is using a Carrier Routing System (CRS) Performance Route Processor (PRP), , Cisco Route Processor A (RP-A), or a Cisco Route Processor B (RP-B), the show inventory all command can be issued and filtered with the product ID of the affected card. The following are examples from devices using the CRS-16-PRP-6G (PRP), CRS-16-RP-B (RP-B) and CRS-16-RP (RP-A):

Cisco IOS XR Software Route Processor Denial of Service Vulnerability

Cisco IOS XR Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.

The vulnerability is due to improper processing of fragmented packets by the following:

Cisco CRS 16-Slot Line Card Chassis Route Processor (RP-A)

Cisco CRS 16-Slot Line Card Chassis Route Processor B (RP-B)

Carrier Routing System (CRS) Performance Route Processor (PRP)

Cisco CRS Distributed Route Processor (DRP-B)

An attacker could exploit this vulnerability by sending fragmented packets to a vulnerable system; this vulnerability cannot be triggered by IP traffic traversing a vulnerable device. An exploit could allow the attacker to cause the packets originating on the Route Processor CPU to stop transmitting to the fabric, resulting in a DoS condition.

This vulnerability can be triggered by both IPv4 and IPv6 traffic and does not require a TCP three-way handshake.

This vulnerability has been documented in Cisco bug ID CSCuh30380 (registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2013-5549

This vulnerability is addressed in the same SMU as Cisco bug ID: CSCtz62593

Successful exploitation of the vulnerability could cause the route processor on an affected device to stop transmitting packets from the route processor CPU to the fabric. As a result, the affected RP-A, RP-B, PRP, or DRP-A will experience a DoS, failing to transmit all of its route processor-based protocols (for example, Intermediate System-to-Intermediate System, Border Gateway Protocol, ICMP).

When considering software upgrades, customers are advised to consult the Cisco Security Advisories, Responses, and Notices archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

Cisco has released free software updates that address the vulnerability described in this advisory. Prior to deploying software, customers are advised to consult their maintenance providers or check the software for feature set compatibility and known issues that are specific to their environments.

Note: This vulnerability is addressed in the same SMU as Cisco bug ID: CSCtz62593

For Cisco IOS XR Software running on the CRS Performance Route Processor, the vulnerability is present in Cisco IOS XR Software Releases 4.0.0 to 4.2.0. The following SMUs for CRS PRP series devices correct this vulnerability:

For Cisco IOS XR Software running on CRS RP-A, RP-B, or DRP-B the vulnerability is present in Cisco IOS XR Software Releases 3.3.0 to 4.2.0 inclusive for CRS-1 and Cisco IOS XR Software Releases 4.0.0 to 4.2.0 for CRS-3. The following SMUs for CRS series devices correct this vulnerability:

Customers with Cisco products that are provided or maintained through prior or existing agreements with third-party support organizations, such as Cisco Partners, authorized resellers, or service providers, should contact that organization for assistance with the appropriate course of action.

The effectiveness of any workaround or fix depends on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Because of the variety of affected products and releases, customers should consult their service providers or support organizations to ensure that any applied workaround or fix is the most appropriate in the intended network before it is deployed.

Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC):

+1 800 553 2447 (toll free from within North America)

+1 408 526 7209 (toll call from anywhere in the world)

email: tac@cisco.com

Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade. Customers without service contracts should request free upgrades through the TAC.

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